Mr Stanhope, Canberra's longest serving chief minister, said Richard Farmer's emergence, the mood against Chief Minister Andrew Barr, and the "it's time" factor were a dangerous combination.

The assumption that a protest vote would flow to the Greens, resulting in another Labor-Green coalition government was not well founded, he said.

The only other Labor-Green coalition government in Australian history was in Tasmania, and both parties had been comprehensively defeated in 2014, Labor losing three of its 10 seats and the Greens losing two of their five. The Liberals won 15 seats.

Tasmania has the same Hare Clark voting system as Canberra, with 25 seats across five electorates.

"When the electorate turned and was determined to punish, their coalition partner was punished equally or more severely …

"In the language of Clive Hamilton, the baseball bats came out and they were used on the Greens, I think, with more vehemence than they were used on Labor and the Liberals won a resounding victory," Mr Stanhope said, referring to Mr Hamilton's comment after the government's weekend backdown on the redevelopment bid for Manuka Oval that the "baseball bats" were out for Mr Barr.

Mr Stanhope has organised a public forum on Thursday on the falling support for major parties and the rise of minors, asking whether the distrust of politicians nationally and internationally, giving rise to Donald Trump in the US, and the likes of Pauline Hanson and Nick Xenophon Australia, was reflected in Canberra.

Mr Stanhope said in 2008 in the ACT, the Greens had benefited from the protest vote, winning four seats. But in 2012, they had lost three of those. Another anti-Labor swing would come in October. "Why would you think that is going to go to the Greens? It didn't in 2012. The Greens were the biggest losers," he said, questioning whether people who voted Green to protest Labor's "pragmatism" would "forgive" Mr Rattenbury.

Mr Rattenbury had "behaved like a loyal member of the Labor cabinet" and left it very late in the day to distinguish himself.

"He hasn't really given those that are of a mind to punish the government much reason to excuse him or not to mete out the angst that they may be feeling against the government on the Greens as well."

Mr Stanhope also pointed to a loss of political memory. With the resignation of Simon Corbell at this election, none of the Labor team had been in opposition. And with the loss of Brendan Smyth in July, none of the Liberal team had been in government.

Mr Stanhope was in opposition in 1998, when the minority Liberal government was supported by three crossbenchers, Michael Moore, Paul Osborne and Dave Rugendyke.

"Behind the success of two of the independents of that era was Richard Farmer," Mr Stanhope said. "The very person who was part of that process is back."

Mr Farmer, who is lobbying for the clubs against poker machines in the casino, has set up a political party, Canberra Community Voters, but is yet to announce candidates.

Michael Moore, a successful independent for 12 years, said there was little doubt voters were looking for an alternative.

"There is disenchantment across the spectrum. The federal Liberals are not helping the local Liberal party, Labor's incumbency is not doing them any favours, and middle-of-the-road voters are largely not ready to vote Green ... That's the fertile ground on which independents can run."